Duplexer/Multiplexer Having Filters that Include at Least One Band Reject Filter

ABSTRACT

A wireless communications device includes an antenna, a multi-port path selection structure having an antenna port connected to the antenna, and plural ports connected to respective one or more receive and transmit paths of the wireless communications device. The multi-port path selection structure has a transmit band reject filter connected to the transmit path and a second filter connected to the receive path.

TECHNICAL FIELD

The invention relates generally to a duplexer/multiplexer that hasfilters including at least one band reject filter.

BACKGROUND

Wireless communications devices, such as wireless terminals or wirelessbase stations, include wireless transceivers to perform wirelesscommunications, such as radio frequency (RF) communications. A wirelesscommunications device can include a duplexer (or multiplexer) to allowsimultaneous transmission and reception in different frequency bandsusing the same antenna while ensuring that relatively high powertransmit signals transmitted by the wireless transceiver do not swamprelatively low power receive signals received by the wirelesstransceiver.

A duplexer has an antenna port (for connection to an antenna), a receiveport (to receive a signal from the antenna port) and transmit port (totransmit a signal to the antenna port). A multiplexer has an antennaport and one or more receive ports and one or more transmit ports. Notethat a duplexer is a type of multiplexer.

A duplexer or multiplexer can include bandpass filters implemented withacoustic-type resonators. Conventional duplexers/multiplexers includingbandpass filters implemented with acoustic-type resonators haverelatively limited maximum power handling capabilities, which canprevent use of such conventional duplexers/multiplexers in high-power,high-frequency applications, such as in Worldwide Interoperability forMicrowave Access (WiMax) applications or Long-Term Evolution (LTE)applications. WiMax is based on the IEEE (Institute of Electrical andElectronics Engineers) 802.16 Standard (as amended by the IEEE 802.16eor IEEE 802.16e-005). WiMax is able to provide broadband wirelessconnectivity for mobile stations at relatively high data rates. LTE is atechnology that provides an enhancement to the Universal MobileTelecommunications System (UMTS) technology. LTE is described in 3GPP TS23.401 and 23.402.

In conventional duplexers/multiplexers that employ bandpass filters withacoustic-type resonators, high-power and high-frequency communicationscan cause ultrasonic vibration in metallic electrodes of theacoustic-type resonators, which can lead to a phenomenon referred to asacousto-migration, in which metal grain boundaries in the resonatorsmigrate. The acousto-migration phenomenon can reduce the lifetime of thefilters. Therefore, such filters may not survive for a desirable lengthof time at desired power levels and frequencies that may be required incertain types of wireless networks.

SUMMARY

In general, according to an embodiment, a wireless communications deviceincludes an antenna and a multi-port path selection structure (e.g., aduplexer or multiplexer) having an antenna port connected to theantenna, and plural ports connected to respective receive and transmitpaths of the wireless communications device. The multi-port pathselection structure has a band reject filter connected to the transmitpath and a second filter connected to the receive path.

Other or alternative features will become apparent from the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless communications device thatincludes a duplexer or multiplexer according to an embodiment.

FIG. 2 is a schematic diagram of a conventional duplexer that includesbandpass filters connected to a receive port and a transmit port of theduplexer.

FIG. 3 is a graph illustrating the transmit and receive bands providedby the bandpass filters of FIG. 2.

FIG. 4 is a schematic diagram of a duplexer that includes a receivefilter connected to a receive port, and a band reject filter connectedto a transmit port, according to an embodiment.

FIG. 5 is a graph illustrating the transmit and receive bands providedby the filters of FIG. 4.

FIG. 6 illustrates acoustic-type resonators arranged in a ladder-typeconfiguration for implementing a band reject filter for use in aduplexer or multiplexer according to an embodiment.

FIG. 7 is a graph illustrating the resonance and anti-resonancefrequencies of the resonators of FIG. 6.

FIG. 8 is a schematic diagram of a duplexer according to anotherembodiment that includes a band reject filter connected to a receiveport, and a band reject filter connected to a transmit port.

FIG. 9 is a graph illustrating the transmit and receive bands providedby the filters of FIG. 8.

FIG. 10 is a schematic diagram of a multiplexer that includes bandpassfilters connected to receive ports, and band reject filters connected totransmit ports, according to another embodiment.

FIG. 11 is a graph illustrating the transmit and receive bands providedby the filters of FIG. 10.

FIG. 12 is a schematic diagram of a multiplexer that includes bandpassfilters connected to receive ports, and a band reject filter connectedto a transmit port, according to a further embodiment.

FIG. 13 is a graph illustrating the transmit and receive bands providedby the filters of FIG. 12.

FIG. 14 is a schematic diagram of a band reject filter formed ofcascaded band reject filter units to provide multiple reject bands,according to an embodiment.

FIG. 15 is a graph illustrating the multiple reject bands provided bythe band reject filter of FIG. 14.

FIG. 16 is a schematic diagram of a duplexer according to a furtherembodiment that includes a bandpass filter connected to a receive port,and a band reject filter connected to a transmit port.

FIG. 17 is a graph illustrating the transmit and receive bands providedby the filters of FIG. 16.

FIG. 18 is a schematic diagram of a duplexer according to yet a furtherembodiment that includes a band reject filter connected to a receiveport, and a band reject filter connected to a transmit port.

FIG. 19 is a graph illustrating the transmit and receive bands providedby the filters of FIG. 18.

FIG. 20 is a schematic diagram of a multiplexer that includes a bandreject filter connected to a receive port, and a band reject filterconnected to a transmit port, according to a further embodiment.

FIG. 21 is a graph illustrating the transmit and receive bands providedby the filters of FIG. 20.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of some embodiments. However, it will be understood bythose skilled in the art that some embodiments may be practiced withoutthese details and that numerous variations or modifications from thedescribed embodiments may be possible.

In accordance with some embodiments, a multi-port path selectionstructure for use in a wireless communications device is provided thathas an antenna port connected to an antenna of the wirelesscommunications device, and plural ports connected to respective receiveand transmit paths of the wireless communications device. Examples ofthe wireless communications device include a wireless terminal (mobilestation), a wireless base station, and other devices that are capable ofperforming wireless communications.

A multi-port path selection structure can be a duplexer or amultiplexer. Generally, a multi-port path selection structure includescircuitry to selectively route signals that are communicated alongtransmit and receive paths of the wireless communications device. Suchcircuitry can receive a signal from the antenna of the wirelesscommunications device, and route the received signal to the receive pathof the wireless communications device. Similarly, the multi-port pathselection structure can route a transmitted signal from transmissioncircuitry in the transmit path of the wireless communications device tothe antenna. The “routing” of the received and transmitted signals isaccomplished by use of filters provided in the multi-port path selectionstructure, where the filters are designed to pass signals in respectivereceive and transmit frequency bands. In accordance with someembodiments, the filter connected to the transmit path is a band rejectfilter, and the filter connected to the receive path can either be abandpass filter or band reject filter.

A duplexer has an antenna port connected to the antenna of the wirelesscommunications device, and a single receive port and a single transmitport for connection to respective receive and transmit paths of thewireless communications device. A multiplexer includes an antenna portfor connection to the antenna of the wireless communications device, andtwo or more ports connected to respective receive and transmit paths.Note that a duplexer is a type of multiplexer.

A multiplexer can have plural receive ports (corresponding to differentreceive frequency bands) and/or plural transmit ports (corresponding todifferent transmit frequency bands). The multiple receive ports can beconnected to one or plural receive paths in the wireless communicationsdevice. The multiple transmit ports can be connected to one or pluraltransmit paths in the wireless communications device. Note that it ispossible for multiple receive frequency bands and/or multiple transmitfrequency bands to share just one receive path or transmit path,respectively, since a wireless communications device normally operatesat just a single receive or transmit frequency band at any given time.Alternatively, separate paths in the wireless communications device canbe provided for different receive frequency bands or different transmitfrequency bands.

FIG. 1 illustrates an exemplary wireless communications device 100 thatincludes a duplexer or multiplexer 102 according to an embodiment. Inthe ensuing discussion, reference is made to “multiplexer” 102, althoughit is to be understood that the discussion applies equally to aduplexer. The wireless communications device 100 has an antenna 104 forcommunicating radio frequency (RF) signals with another communicationsdevice. For example, the wireless communications device 100 can be awireless terminal (e.g., mobile station) to communicate wirelessly witha wireless base station. Alternatively, the wireless communicationsdevice 100 can be base station for communicating with a wirelessterminal.

The wireless communications device can be used in a wirelesscommunications network, such as a WiMax (Worldwide Interoperability forMicrowave Access) network, a Long-Term Evaluation (LTE) network, or anyother type of network. Reference to LTE is to any technology based onLTE, such as defined by current standards 3GPP TS 23.401 and 23.402 orany subsequent standard. Reference to LTE can also refer to anysubsequent standard derived from an evolution of LTE, whether or notsuch subsequent standard is referred to as “LTE” by name.

The multiplexer 102 has an antenna port 106 that is connected to theantenna 104. The antenna port 106 of the multiplexer 102 is “connected”to the antenna 104 either directly or indirectly (through othercircuitry).

The multiplexer also has a receive port 108 for connection to a receivepath 110 of the wireless communications device 100, and a transmit port112 for connection to a transmit path 114 of the wireless communicationsdevice. The receive path 110 includes receive circuitry 116 to receive asignal from the antenna 104 through the multiplexer 102. The transmitpath 114 includes transmit circuitry 118 to generate a transmit signalto be sent through the multiplexer 102 onto the antenna 104.

The multiplexer 102 has filters 120 and 122 for passing signals in thereceive and transmit frequency bands, respectively. Also shown in dashedprofile is another filter 124 and another port 126, where the otherfilter 124 and port 126 can be connected to a transmit path or a receivepath, depending upon the specific configuration of the wirelesscommunications device 100.

A conventional duplexer 10 is depicted in FIG. 2, where the conventionalduplexer 10 has an antenna port 12, a receive port 14 (that is connectedto a receive path of a wireless communications device), and a transmitport 16 (that is connected to a transmit path of the wirelesscommunications device). The conventional duplexer 10 uses bandpassfilters (BPFs) 18 and 20 connected to the receive and transmit ports 14and 16, respectively. The bandpass filters 18 and 20 can be implementedwith acoustic-type resonators.

FIG. 3 is a graph of the transmit frequency band 22 and receivefrequency band 24 provided by the bandpass filters 20 and 18,respectively. The graph of FIG. 3 plots insertion loss (in terms ofdecibel or dB) as a function of frequency. Insertion loss is thedecrease in signal power resulting from insertion of a device in acommunications path. As discussed above, the bandpass filters 18 and 20of a conventional duplexer such as duplexer 10 are subject todeterioration caused by the acousto-migration phenomenon at high powerand high frequencies.

In accordance with some embodiments, instead of using bandpass filters18 and 20 in the duplexer 10 as conventionally done, a duplexer 200(depicted in FIG. 4) can be provided that includes a band reject filter202 connected to a transmit port of the duplexer 200, and a receivefilter 204 connected to a receive port of the duplexer 200. Both theband reject filter 202 and receive filter 204 are connected to anantenna port. The receive filter 204 can either be a bandpass filter ora band reject filter, in accordance with some embodiments.

Typically, the transmit signals that are sent from the transmit port tothe antenna port through the duplexer 200 are associated with relativelyhigh power, while the receive signals communicated from the antenna portto the receive port through the duplexer 200 are associated withrelatively low power. The receive filter 204 operates to protect thereceive port (and receive circuitry connected to the receive port)against the high-power transmit signals communicated through theduplexer 200.

Note that with the band reject filter 202, the acoustic vibration isrelatively strong in the reject band, but relatively weak in the passband of the band reject filter. This enables the band reject filter 202to handle relatively high power transmit signals with reducedacousto-migration issues. Moreover, another characteristic of a bandreject filter is that it has lower phase distortion and less ripple inthe pass band, as compared to a bandpass filter.

Assuming the receive filter 204 is implemented with a bandpass filter,then the receive and transmit frequency bands are depicted in FIG. 5,which plots insertion loss as a function of frequency. The bandpassfilter 204 provides a pass band 302—any signal having a frequency belowor above the pass band 302 is attenuated or rejected by the bandpassfilter 204. The band reject filter 202 provides a reject band 304—anysignal having a frequency within the reject band 304 is attenuated orrejected, and any signal having a frequency above or below the rejectband 304 is passed through the band reject filter 202. The pass band 302and reject band 304 of FIG. 5 overlap. The pass band for the transmitpath provided by the band reject filter 202 is represented by referencenumerals 306A and 306B, which are on the two sides of the reject band304 (and of the pass band 302 provided by the bandpass filter 204).

In the receive direction, the bandpass filter 204 passes a signal fromthe antenna port to the receive port of the duplexer 200 if the signalhas a frequency within the receive band 302. On the other hand, in thetransmit direction, the band reject filter 202 passes a signal having afrequency outside the reject band 304 through the band reject filter 202from the transmit port to the antenna port.

A band reject filter can be implemented with acoustic-type resonatorsRES1 and RES2 arranged in a ladder-type configuration, as depicted inFIG. 6. The ladder-type configuration includes a first acoustic-typeresonator RES1 (referred to as “series resonator”) connected in seriesbetween two ports PORT 1 and PORT2, and a second acoustic-type resonatorRES2 (referred to as “shunt resonator”) connected between PORT2 andground. Note that in the ladder-type configuration, there can be two (ormore) series resonators between PORT1 and PORT2, and two (or more) shuntresonators connected between nodes of the filter and ground.

Each of the resonators RES1 and RES2 can be any one of a surfaceacoustic wave (SAW) resonator, a thin film bulk acoustic resonator(FBAR), a bulk acoustic wave (BAW) resonator, or any other type ofacoustic-type resonator. The BAW resonator can be a surface mountedresonator (SMR)-type BAW resonator.

The series resonator RES1 of FIG. 6 is designed to present a highimpedance at the reject band 304 of interest. The series resonator RES1is configured to be anti-resonance at a reject band frequency (theanti-resonance frequency for the series resonator RES1 is depicted inFIG. 7, according to one example), which means that the series resonatorRES1 presents a high impedance at the anti-resonance frequency. Incontrast, the shunt resonator RES2 is configured to provide a lowimpedance at a reject band frequency (a frequency within reject band304). This is achieved by designing the shunt resonator RES2 to be at ornear resonance in the reject band 304. The resonance frequency of theshunt resonator RES2 is represented as 404 in FIG. 7.

The resonance frequency of series resonator RES1 is represented as 406in FIG. 7, while the anti-resonance frequency of the shunt resonatorRES2 is represented as 408 in FIG. 7. The resonance frequency 406 of theseries resonator RES1 is immediately below the reject band 304 and isbetween the pass band 306A and the reject band 304 of the band rejectfilter—at the resonance frequency 406, the series resonator RES1 has alow impedance. In the pass band 306A, the shunt resonator RES2 simplypresents a capacitive load to ground.

The anti-resonance frequency 408 of the shunt resonator RES2 isimmediately above the reject band 304 and is between the reject band 304and the pass band 306B—at the anti-resonance frequency 408, the shuntresonator RES2 presents a high impedance to ground. However, in the passband 306B, the series resonator RES1 presents a capacitive seriesimpedance. At frequencies much above or below the reject band 304, theseries and shunt resonators simply behave as high-Q capacitors.

In this manner, the overall effect of the filter provided by resonatorsRES1 and RES2 is to provide a high impedance for signals passing betweenports PORT1 and PORT2 having frequencies in the reject band 304.

FIG. 8 shows an implementation of the duplexer 200 in which the receivefilter 204 is implemented with a band reject filter (instead of abandpass filter as depicted in FIG. 4). In this configuration, both thereceive and transmit ports of the duplexer 200 are connected to bandreject filters.

As depicted in FIG. 9, the band reject filter 202 for the transmit portis associated with the transmit reject band 304, while the band rejectfilter 204 for the receive port has a receive reject band 402. The bandreject filter 204 allows a signal having a frequency outside the receivereject band 402 to be passed through the band reject filter 204, whereasthe band reject filter 202 allows a signal having a frequency outsidethe transmit reject band 304 to pass through the band reject filter 202.

FIG. 10 shows a multiplexer 500 that has an antenna port, two receiveports (RX1 port and RX2 port), and two transmit ports (TX1 port and TX2port). Note that the two receive ports can be connected to just onereceive path (and the associated receive circuitry, such as circuitry116 in FIG. 1), or alternatively, the two receive ports can be connectedto two different receive paths. Similarly, the transmit ports can beconnected to just one transmit path (and the associated transmitcircuitry, such as 118 in FIG. 1), or alternatively, the transmit portscan be connected to multiple transmit paths. In other implementations,the multiplexer 500 can have more than two transmit ports and/or morethan two receive ports. The different receive ports are associated withdifferent receive frequency bands, and the different transmit ports areassociated with different transmit frequency bands.

The receive ports of the multiplexer 500 are connected to correspondingbandpass filters 502 and 504, whereas the transmit ports are connectedto band reject filters 506 and 508. Each of the bandpass filters andband reject filters 502, 504, 506, and 508 is connected to the antennaport of the multiplexer 500.

As depicted in the graph of FIG. 11, a receive pass band 602 correspondsto the pass band provided by the bandpass filter 502 for the RX1 port,and a receive pass band 604 is provided by the bandpass filter 504 forthe RX2 port.

A transmit reject band 606 is provided by the band reject filter 506 forthe TX1 port, and a transmit reject band 608 is provided by the bandreject filter 508 for the TX2 port.

While FIG. 10 shows separate band reject filters 506 and 508 to providetwo respective reject bands 606 and 608 (FIG. 11), note that a singleband reject filter can be used instead, such as band reject filter 702in a multiplexer 700 depicted in FIG. 12, to provide multiple rejectbands. The multiplexer 700 has one transmit port connected to the bandreject filter 702.

The chart of FIG. 13 depicts receive pass bands 602 and 604 and transmitreject bands 606 and 608 that are the same as those depicted in FIG. 11,except that the reject bands 606 and 608 of FIG. 13 are provided by oneband reject filter 702 (FIG. 12), instead of two distinct band rejectfilters 506 and 508 (FIG. 10).

The band reject filter 702 includes multiple cascaded band reject filterunits to provide the multiple reject bands 606 and 608. Cascadingmultiple band reject filter units means that the band reject filterunits are connected in series. For example, as depicted in FIG. 14,three band reject filter units 802, 804, and 806 are connected in series(cascaded) between PORT1 and PORT 2. Each of the band reject filterunits 802, 804, and 806 defines a respective reject band, as depicted inFIG. 15. The band reject filter unit 802 provides reject band 902, theband reject filter unit 804 provides reject band 904, and the bandreject filter unit 806 provides reject band 906. Each of the band rejectfilter units contains an arrangement of resonators; in the embodiment ofFIG. 14, each band reject filter unit includes two series resonators andtwo shunt resonators arranged in the ladder-type configuration. Toprovide the two transmit reject bands 606 and 608 of FIG. 13, two bandreject filter units (e.g., any two of 802, 804, and 806) can beconnected in series (cascaded) to form the band reject filter 702. Inother implementations, the resonators of all band reject filter unitscan be arranged in a mixed configuration for their locations in theladder-type structure, namely each of the band reject filter units canhave its resonators distributed in the entire filter structure and doesnot have to have all its resonators arranged together.

FIG. 16 shows an alternative embodiment of a duplexer 1000 that has aband reject filter 1002 for the transmit port that provides multiplereject bands 1102, 1104, and 1106 (FIG. 17). The band reject filter 1002is thus able to block signals having frequencies in any of the rejectbands 1102, 1104, and 1106.

A bandpass filter 1004 connected to the receive port of the duplexer1000 provides a pass band 1108 (FIG. 17).

FIG. 18 shows another embodiment of a duplexer 1200 that includes bandreject filter 1202 connected to a receive port of the duplexer 1200, andband reject filter 1204 connected to the transmit port of the duplexer1200. Each of the band reject filters 1202 and 1204 provides multiplereject bands, as depicted in FIG. 19. The band reject filter 1202 forthe receive port provides reject bands 1312, 1310, and 1314, while theband reject filter 1204 for the transmit port provides reject bands1304, 1302, and 1306.

FIG. 20 shows another embodiment of a multiplexer 1300 that includes afirst band reject filter 1302 for the RX1, RX2, . . . , RXn port, and asecond band reject filter 1304 for the TX1, TX2, . . . , TXn port. Theband reject filter 1302 provides reject bands 1402, 1404, and 1406,whereas the band reject filter 1304 provides reject bands 1408, 1410,and 1412, as depicted in FIG. 21.

In the foregoing description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details. While the invention has been disclosedwith respect to a limited number of embodiments, those skilled in theart will appreciate numerous modifications and variations therefrom. Itis intended that the appended claims cover such modifications andvariations as fall within the true spirit and scope of the invention.

1. A wireless communications device comprising: an antenna; a multi-portpath selection structure having an antenna port connected to theantenna, and plural ports connected to respective one or more receiveand transmit paths of the wireless communications device, wherein themulti-port path selection structure has a transmit band reject filterconnected to the transmit path and a second filter connected to thereceive path.
 2. The wireless communications device of claim 1, whereinthe second filter comprises a bandpass filter.
 3. The wirelesscommunications device of claim 2, wherein the multi-port path selectionstructure further comprises another bandpass filter connected to thereceive path.
 4. The wireless communications device of claim 1, whereinthe multi-port path selection structure is a duplexer.
 5. The wirelesscommunications device of claim 1, wherein the multi-port path selectionstructure is a multiplexer.
 6. The wireless communications device ofclaim 1, wherein the wireless communications device comprises a wirelessmobile station.
 7. The wireless communications device of claim 1,wherein the wireless communications device comprises a wireless basestation.
 8. The wireless communications device of claim 1, wherein thetransmit band reject filter provides multiple reject bands.
 9. Thewireless communications device of claim 8, wherein the second filtercomprises a receive band reject filter.
 10. The wireless communicationsdevice of claim 9, wherein the receive band reject filter providesmultiple reject bands.
 11. The wireless communications device of claim1, wherein the transmit band reject filter includes acoustic-typeresonators.
 12. The wireless communications device of claim 11, whereinthe acoustic-type resonators are selected from among surface acousticwave (SAW) resonators, thin film bulk acoustic resonators (FBAR), andbulk acoustic wave (BAW) resonators.
 13. The wireless communicationsdevice of claim 11, wherein the acoustic-type resonators are arranged ina ladder-type configuration.
 14. The wireless communications device ofclaim 1, wherein the transmit band reject filter has relatively weakacoustic vibration in a pass band of the transmit band reject filter,and relatively strong acoustic vibration in a reject band of thetransmit band reject filter.
 15. A wireless communications devicecomprising: an antenna; a multiplexer having an antenna port connectedto the antenna, at least one receive port connected to at least onereceive path of the wireless communications device, and at least onetransmit port connected to at least one transmit path of the wirelesscommunications device, wherein the multiplexer has a transmit bandreject filter connected to the transmit port and a second filterconnected to the receive port.
 16. The wireless communications device ofclaim 15, wherein the second filter comprises a band reject filter. 17.The wireless communications device of claim 16, wherein the second bandreject filter provides multiple reject bands.
 18. The wirelesscommunications device of claim 15, wherein the transmit band rejectfilter provides multiple reject bands.
 19. The wireless communicationsdevice of claim 15, wherein the band reject filter includesacoustic-type resonators.
 20. A method of enabling wirelesscommunications, comprising: providing an antenna at a wirelesscommunications device; providing a multi-port path selection structurehaving an antenna port connected to the antenna, and transmit andreceive ports connected to respective transmit and receive paths of thewireless communications device; providing a transmit band reject filterto provide a reject band for the transmit port; and providing a secondfilter connected to the receive port.
 21. The method of claim 20,wherein the second filter comprises a second band reject filter.